<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<button id="btn02">click me~</button>
		<script>
			btn02.onclick = function() { //被覆盖
				console.log('first');
			}
			btn02.onclick = function() {
				console.log('second');
			}
		</script>
	</body>
</html>
